Apparatus for separating dirt from aqueous suspensions of pulp fibers



June 5, 1962 SUSPENSIONS OF PULP FIBERS 3 Sheets-Sheet 1 Filed June 22 June 5, 1962 G. H. TOMLINSON n APPARATUS FOR SEPARATING DIRT FROM A QUEOUS SUSPENSIONS OF PULP FIBERS 3 Sheets-Sheet 2 Filed June 22, 1953 7 Vacuwv PUMP I juenlb/ GZETomllitsom/l June 5, 1962 G. H. TOMLINSON n APPARATUS FOR SEPARATING DIRT FROM AQUEOUS SUSPENSIONS 0F PULP FIBERS 5 Sheets-Sheet 5 Filed June 22, 1953 3,037,628 APPARATUS FOR SEPARATING DIRT FROM AQUEOUS SUEaPENSiONS OF PULP FIBERS George H. Tomlinson II, Cornwall, Ontario, Canada, as-

signor to Dominion Tar and Chemical (10., Montreal,

Quebec, Canada, a corporation of Canada Filed June 22, 1953, Ser. No. 363,277 6 Claims. (Cl. 209Z11) This invention relates to a new and efiicient method and apparatus for cleaning an aqueous suspension of pulp or paper-making fibres whereby objectionable foreign material including that usually referred to as dirt" is removed by means of combined centrifugal and shear action in a device which can be classed as a vortex type separator.

The present application is a continuation-in-part of my co-pending application Serial No. 205,655, filed January 12, 1951, now abandoned.

In the conversion of wood or other fibrous material to pulp and paper three main classes of foreign matter and dirt must be considered.

(1) Portions of the wood which have not completely broken down into individual fibres as a result of the chemical and/ or mechanical action. A particle of such material may be relatively large such as an undefibred chip or knot, but when broken down to size such as might be embedded in a sheet of paper it is referred to as a shive.

(2) Pieces of bark which do not disintegrate in cooking and remain as black or dark colorured specks in the final pulp.

(3) Foreign matter of non-fibrous origin that enters the system with the wood or at any subsequent stage, this including sand, pipe-scale, fly-ash, cinders, etc.

Dirt particles can of course be present in a considerable range of sizes. With regard to the minimum size of material referred to as dirt the Technical Association of the Pulp and Paper Industry (frequently referred to as TAPPI) has given (Standard T213) the following definition: Dirt in pulp is defined as any foreign matter which is embedded in a sheet, which has a marked contrasting colour to the rest of the sheet when viewed by reflected light and which has an equivalent area of 0.08 sq. mm. or more. With paper (Standard T437) foreign matter in the sheet is similarly defined with the exception that particles of 0.04 sq. mm. or more are considered as dirt.

On account of the extremely divergent physical character and size of the dirt particles that may be present many varied methods of cleaning have been devised and are conventionally employed in combination in order to obtain a final product which is reasonably uncontaminated with foreign materials that would mar the appearance and serviceability of the final sheet of pulp or paper.

In the manufacture of a bleached chemical pulp, the relatively small percentage of non-disintegrated wood present in the pulp, is normally partially removed by screening. Knots and undefibred chips are first removed by passing the stock through perforated plates, the perforations being about A diameter. The stock is then fine screened, on either fiat screens having slots about 8 to 12 mils wide or on rotary screens having perforations of about 60 mils diameter. The pulp is then bleached, passed over rifilers to settle out heavy dirt, and rescreened, usually through fiat screens similar to those described above. In the paper mill'the stock is normally screened once again and passed through stationary centrifugal cleaners designed to remove particles of high s.g. dirt which the screens and/ or rifliers have failed to catch.

The diameter of a single fibre is of the order of 1 mil and it might be assumed that it would be possible to use slots of but slightly greater width for screening purposes. However, from a practical standpoint it is necessary with fiat screens to have the slots many times greater than ice the fibre width, of the order of about 10 times, and in order to prevent plugging and matting relatively low consistencies are used, the final stock having a consistency of 0.3 to 0.4%. Inasmuch as screens are not completely selective in their action, multiple screening is often used, but in spite of this, some shive will carry through. By cooking the pulp by relatively drastic means the quantity of initial shive is diminished, and in bleaching, further chemical cleaning of shive is obtained due to removal of lignin which binds the fibres together. In addition to chemical cleaning, mechanical attrition is also obtained, this resulting from the action in pumps through the pulp mill, and particularly in the beater, jordan or other refining equipment in the paper mill whereby many of the individual fibres are torn apart. By a balance of multiple screening with chemical and mechanical defibring it is possible to control shive content in the final fine paper to a reasonably low level, with the chemical cleaning normally acting as the control pointthat is, the amount of chemical or temperature or time at the cooking or bleaching stages is increased when the shive count appears to be unreasonably high at any point along the system; this normally results in lower pulp yields and sometimes in excessive degradation in pulp.

The control of bark dirt is an even more serious problem. Whereas the shive is normally somewhat longer than it is wide this enhancing its chance of being rejected by the screen, bark dirt tends to be random in shape, approaching a sphere. Moreover, it is less susceptible to bleaching out. Thus conventionally, to obtain a fine paper free of bark dirt, it is necessary to take extra precautions with the wood used. This means recycling of logs through the barking drums to remove all traces of adhering bark. However, logs contain ingrown bark around knots, etc., and many mills resort to treatment with rossers, woodpeckers, etc., to remove both wood and bark around the most seriously affected areas. When the wood, even after such drastic cleaning, is chipped, it is found that the chipper dust contains considerable bark fragments, and a fraction passing a A; inch mesh, which amounts to about 1% to. 3% of the wood, is normally screened off and discarded to obtain a reduced bark speck count in the final pulp.

The minimization of high specific gravity extraneous dirt is normally accomplished in three ways, namely, by taking precautions to avoid its entry to the system by providing for thorough Washing of the logs, filtration of process water, etc., by riffiing in the pulp mill, and by the use of stationary centrifugal cleaning tubes in the paper mill, all three methods usually being used in combination.

It is thus apparent that through direct and indirect expense the cost involved in producing a clean sheet of pulp or paper is extremely high. The individual conventional means of cleaning are normally specific for one type and/ or size of dirt, and even for that type and/or size the efiiciency is often low, while for types and sizes of dirt other than that for which the equipment was designed, the efficiency may be essentially zero.

By the methods of the present invention shive, bark dirt and high specific gravity dirt can all be removed simultaneously from the fibre and, within certain wide limitations, this is accomplished regardless of the size of the particles. Furthermore, by the choice of certain dimensions of the individual cleaning units, which will modify the flow of the separated dirt within the unit, it has been found possible to extend the range in the size of particles removed in one direction or the other as may be desired.

This combination of results, which has been obtained in a vortex type separator, has never been described as having been accomplished by any previously available means or device.

It has heretofore been considered axiomatic that in a vortex separator the smaller the diameter of the unit the greater the centrifugal force, and therefore the greater the separation factor that will be obtained. Unexpectedly I have found that the separation factor can be increased by increasing the diameter of the unit providing that the inlet and outlet size, the cone angle, and the pressure differential are not altered. This results in increased efficiency for the removal of all types of dirt present in pulp suspensions, including wood dirt, shive, etc. Unexpectedly such a separator has a very much higher efiiciency in the removal of shive than units having dimensions in the same proportion but of smaller diameter even though the latter will develop greater centrifugal force and may be more efiicient in removing extremely small particles of a size not normally classed as dirt.

The different action obtained by units of different size and proportion results not only from the centrifugal force but also from the shear rates developed in the unit. The ratio between these may be adjusted to obtain any given desired result by the proper sizing and proportioning of the dimensions of the unit as will hereinafter be described.

By the method of the present invention an aqueous suspension of the pulp at a consistency that may be in the range of 0.4% to 1.2% is introduced under pressure through a pipe set tangentially to a cylinder, one end of which is connected to the large end of a truncated cone of about 10 to 30 contained angle having an opening of at least one half inch at its truncated apex through which a suspension of the concentrated dirt and a small portion of the fibre is discharged, while the cleaned pulp is dis charged through an outlet in axial alignment with the apex, this outlet extending through the otherwise closed end of the cylindrical section. The small percentage of fibre rejected with the dirt can be subsequently reclaimed as will be hereinafter described.

Proceeding now to a more detailed description of the invention reference will be made to the accompanying drawings wherein:

FIG. 1 is a fragmentary longitudinal sectional view illustrating one embodiment of the present invention,

FIG. 2 is a longitudinal sectional view illustrating a modification of the structure of the reject outlet,

FIG. 3 is a longitudinal sectional view of the structure at the accepted stock outlet,

FIG. 4 is a sectional view of a modification of the rejects outlet,

FIG. 5 is a sectional view along the line -10 of FIG. 4,

FIG. 6 is a fragmentary sectional view illustrating a modification of the invention whereby materials lighter than water can be removed simultaneously with dirt of high specific gravity.

In continuation application Serial No. 694,479, now Patent 2,878,934, issued March 24, 1959, there is disclosed a separator comprising a cone section having a tangential inlet at the upper end thereof, a rejects discharge outlet at the apex end and an accepted stock outlet at the base. There is provided a vacuum chamber in communication with the apex outlet which affords a liquid free space into which air entering through the liquid free core is discharged together with a stream of suspension containing dirt particles.

There is shown in FIG. 1 herein a modification of the separator disclosed in Patent 2,878,934 and it can be seen that the rejected material is discharged directly into a vacuum chamber provided by a casing 53 arranged immediately below the dirt discharge aperture 6. The solid and liquid components of the rejects are continuously withdrawn from casing 53 through a drain pipe 54 in which a liquid seal 55 is maintained so that said casing provides a liquid-free space into which the rejects are discharged from cone section 5, said space being maintained under sub-atmospheric pressures with the result that a suction is created in the previously mentioned liquid-free space 21, extending along the axis of cone section 5 within the upward spiralling stream of clean stock passing to outlet 9. The liquid seal may be maintained by means of a barometric leg from which the rejected stock will drain, or by means of a pump fitted with a level control on the suction side. It has been found that, when the apparatus of the present invention is operated in conformity with this modification, the rate of flow through the rejects discharge aperture 6 is approximately one-third greater than when discharged into atmosphere. This results from a decreased diameter of the liquid-free axial core due to its decreased pressure, and the diameter of the aperture 6 can be adjusted to give the desired rate of rejection when operating under these conditions. This modification prevents entrainment of air in the accepted stock.

A satisfactory method of simultaneously removing the rejected stock from the unit and maintaining a vacuum in the liquid-free vortex column is shown in FIGURE 1. The cone section 5 of the separator terminates at orifice 6 which is centered in a vertical pipe section 56, sealed to the cone at its upper end 57. The vertical pipe 56 is connected at its lower end to horizontal pipe 58 which is sealed at one end 59 and connects at the other end to a commercially available water ejector 60. The ejector is actuated by water under pressure through pipe 61 and valve 62 and discharges under submergence through pipe 63 into box 64, the liquid level of which is controlled by valve 65, through which the additional dilution water is added. The diluted rejects in box 64 may be pumped through pump 66 to a secondary cleaner not shown. If desired, a vacuum line 67 may also be connected at the upper section of the liquid-free column 21 at the top of cleaned stock outlet pipe 9 of the vortex separator. Vacuum line 67 may be centered on the liquid-free column by insertion through elbow 16, which is connected to outlet pipe 9 through reducer 15. Vacuum line 67 may be connected to any suitable source of suction. For example, it may be connected to evacuated pipe 58 by means of connecting piping 68. The accepted cleaned and deaerated stock is delivered from elbow 16 through pipe 19 to its point of use.

Entrained air carried in the stock through tangential inlet pipe 8 to the vortex separator head piece 7 is immediately driven towards the centre of the unit where it carries down outlet pipe 9 to its lower end where it passes to the liquid-free column 21. When vacuum pipe 67 is used, the separated air will normally follow this route to evacuated pipe 58, but if pipe 67 is not used, most of the separated air will follow the alternate route down the liquid-free column to evacuated pipe 58. The separated air will be drawn through ejector and discharged to the atmosphere through the liquid seal in box 64. It has been found that a Penberthy No. 7 ejector when operating at an actuating water pressure of 45 pounds per square inch, this requiring 45 United States gallons per minute, will remove the liquid and solids rejects from a unit of 12 inches diameter with 2 inches diameter stock inlet and outlet and /2 inch rejection orifice, while at the same time maintaining a vacuum in the liquid-free column of 29 inches of mercury when referred to an atmospheric pressure of 29.9 inches (2.2 centimetres of mercury absolute pressure). It should be noted that in spite of this high vacuum maintained in the liquid-free column, there is sufficient energy in the rotating column of liquid leaving outlet pipe 9 to allow delivery of the cleaned stock against atmospheric pressure or even to elevate the stock to an upper fioor should this be required.

If it is desired to remove dissolved air in addition to the entrained air, the modification shown in FIGURE 3 may be used. Cleaned-stock outlet pipe 9 of the vortex separator is extended by pipe 69 into spray chamber 70 consisting of a cylindrical pipe section set at right angles to the axis of the unit and sealed at both ends 71 and 72. Spray chamber 70 is connected by line 73 to a suitable vacuum pump, and stock is drawn from the evacuated chamber by means of drain pipe 74. The lower end of the liquid-free column is sealed from atmosphere by suitable means. The rotational motion of the stock emerging from outlet pipe '69 results in the formation of a hollow cone spray in which the liquid is broken into small droplets thus facilitating the removal of dissolved air by means of the vacuum. The droplets hitting the walls of spray chamber 70 drain down and out through drain connection 74. It is desirable to set spra-y chamber 70 at right angles to the axis of the cleaner, since this prevents a rotational motion in the spray chamber, which would otherwise submerge the outlet of pipe 69 thus preventing the formation of spray.

Since the rotational energy of the liquid leaving the vortex-separator is dissipated in forming this spray, it is not possible to deliver directly to atmosphere through drain 74. When the stock is removed from spray chamber 70 by suitable means and vacuum is applied, then the differential across the separator is increased by approximately one atmosphere as compared with the type of operation previously described. Thus if the unit is set sufficiently high to provide a barometric leg for drain line 74-, the additional pressure required to elevate the stock to this height is compensated for by the fact that the unit discharges into vacuum. With this arrangement, the rejects could also be discharged through a barometric leg as shown in FIGURE 2 and thus only the one pump having the characteristics required for normal operation would be required.

When the height of the building does not allow the use of a barometric leg, a centrifugal pump fitted with a valve for controlling a liquid level in spray chamber 70' just below the end of outlet pipe 69 must be used for removing the stock. With this arrangement, the rejects outlet may be arranged as shown in FIGURE 1.

An alternative method of sealing the rejection outlet thus preventing the introduction of air through the liquidfree column is shown in FIGURES 4 and 5.

Cone 5 is brought to an orifice diameter at outlet 6 which is approximately 55 to 75% of the diameter of the cleaned stock outlet. With a 12" diameter unit having a 10 cone, a 7.05 square inch cross section inlet and 3" outlet, a satisfactory diameter at orifice 6 was found to be 1.75 to 2.00 inches, with the former being preferred. Connected to orifice 6 is flaring truncated cone section 75, its base dimension being somewhat greater than the diameter of the cleaned stock outlet pipe, in this case 4 inches. At the base of cone section 75 is a centrally located solid plate 76 connected by radially extending arms 77 to a ring member 77a. Plate 76 is of greater diameter than the orifice 6 having, for example, a diameter of 3 inches. Free access for the flow of suspension past the plate 76 is afforded by the spaces between the radially extending plate-supporting arms 77, said spaces being located immediately adjacent the wall of cone section 75. The ring member 77a, supporting plate 76, is clamped between the base of cone section 75 and the base of a tapering reducer cone section 78 provided at its apex end with an outlet orifice 79. The diameter of the outlet of orifice 79 should be somewhat less than that of orifice 6, in this case a diameter of 0.5 to 0.75 inch being satisfactory. Centrally located in plate 76 is a small vertical projection 80 which may be a bolt fastened through the plate. This centers and stabilizes the terminal location of the liquid-free column 21 which follows down from cone 5 through orifice 6 to plate 76. An air column 81 develops below plate 76 extending to the orifice 79, and a hollow cone spray discharge 11 forms.

With wood pulp stocks, the various types of dirt normally present have a specific gravity greater than that of water and when the proper unit has been selected, will be carried to the cone wall and discharged through the re jection orifice. However, waste paper stocks and some rag stocks may contain pieces of gum rubber, wax, etc.,

which have a specific gravity less than that of Water and thus go to the liquid-gas interface at the central liquidfree column at the axis. Curiously, when operating the separator in the normal Way, some of this material will be found in the rejected stock, and it is believed that this may possibly result from such a rapid movement towards the centre that it breaks through the surface and then drops by gravity through the liquid-free column. However, such removal is not complete, and when such material is present in any considerable concentration, it may be desirable to provide for its positive removal. This can be accomplished by a modification of the arrangement used in FIGURE 1 where pipe 67, replaced by pipe 82 of FIGURE 6, is so enlarged as to include a thin annulus of the tip-flowing stream, together with floating material in addition to the entrained air. In cases where simultaneous deaeration is not required and therefore Where a vacuum would not otherwise be applied, the vortex separator can be mounted in an upside-down position so that the removal of the skimmed surface liquid through pipe 63 will be assisted by gravity. Similar pro vision must be made for removal of such material in the secondary cleaner.

Having thus described the principles and several embodiments of my invention which will allow the removal of undesirable material including that of both higher and lower specific gravity than that of water and of various sizes and shapes, as well as dissolved and/or entrained gases, it will be understood that various modifications may be resorted to within the scope and spirit of the invention as defined by the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

I claim:

1. Apparatus for de-aerat-ing an aqueous suspension of cellulose fibres and separating dirt particles therefrom comprising a conical separating chamber in which the suspension is whirled about a central axis to produce a vortex of conical form having a central liquid-free core, a tangential inlet through which the suspension is continuously fed to the larger end of said chamber to establish and maintain said vortex, a vacuum casing providing a liquid-free space into which the apex end of the separating chamber extends in air-tight connection with the wall structure of said vacuum chamber, an outlet at the apex end of the separating chamber through which a stream of the suspension entraining dirt particles and a minor proportion of the cellulose fibres is discharged into the liquid-free space afforded by said vacuum chamber, a second outlet located at the larger end of the separating chamber in axial alignment with said first mentioned outlet and through which is discharged a second stream of the suspension containing a major proportion of the cellulose fibres and a suction conduit through which air is withdrawn from the liquid-free core of the vortex, said conduit having an end portion thereof extending into the end of said liquid-free core remote from the apex end of the separating chamber.

2. Apparatus for de-aerating an aqueous suspension of cellulose fibres and separating dirt particles and air therefrom comprising a conical separating chamber in which the suspension is whirled about a central axis to produce a vortex of conical form having a central liquidfree core, a tangential inlet through which the suspension is'continuously fed to the larger end of said separating chamber to establish and maintain said vortex, a vacuum casing affording a liquid-free space into which the apex end of the separating chamber extends in air-tight connection with the wall structure of said vacuum casing, an outlet at the apex end of said separating chamber through which a stream of the suspension entraining dirt particles and a minor proportion of the cellulose fibres is discharged into the liquid-free space afforded by said vacuum casing, means for withdrawing said suspension from said vacuum casing, a spray chamber affording a liquid-free space in the upper portion thereof, a second outlet at the larger end of the separating chamber in axial alignment with said first mentioned outlet and through which a second whirling stream of the suspension containing a major proportion of the cellulose fibres is whirled directly through said outlet into the liquid-free space of said spray chamber to thereby effect separation of air including dissolved air from said second stream of the suspension, a conduit through which the liquidfree space of said spray chamber is connected to a source of suction and means for withdrawing the suspension from said spray chamber including provision for maintaining a pool of the suspension in said spray chamber to seal the liquid-free space therein from atmosphere.

3. Apparatus for separating dirt particles from an aqueous suspension of cellulose fibres comprising a conical separating chamber in which the suspension is Whirled about a central axis to produce a vortex of conical form having a central liquid-free core, a tangential inlet through which the pulp suspension is continuously fed into the larger end of said chamber to establish and maintain said vortex, an outlet at the apex end of said chamber through which a portion of the suspension, entraining dirt particles together with a minor proportion of the cellulose fibres, is continuously discharged from said chamber, a second outlet at the larger end of said chamber in axial alignment with said first mentioned outlet and through which a second stream of the suspension containing a major proportion of the cellulose fibres is continuously discharged from said chamber and means associated with the apex end of said chamber for sealing the adjacent end of the liquid-free core against the admission of external air thereto, said means comprising a flaring truncated cone section open at both ends and having its apex end secured to the apex end of said chamber, a second tapering reducing cone section of truncated form having its base portion secured to the base portion of said first mentioned truncated cone section, the opening at the apex end of the reducing cone section being substantially smaller than the outlet opening at the apex end of said chamber and a solid plate-like member centered within said cone sections and having a diameter greater than the diameter of the opening at the apex end of said chamber, there being flow passages provided between said plate-like member and said cone sections to provide for the flow of suspension past said plate member to and through the opening at the apex end of the reducing cone section.

4. Apparatus for de-aerating an aqueous suspension of cellulose fibres and separating dirt particles therefrom, comprising a conical separating chamber in which the suspension is whirled about a central axis to produce a vortex of conical form having a central liquid-free core, a tangential inlet through which the pulp suspension is continuously fed into the larger end of said chamber to establish and maintain said vortex, an axial outlet at the apex end of said chamber, a vacuum chamber alfording a liquid-free space into which air entering said liquid-free core is discharged together with a stream of the suspension containing dirt particles and a minor proportion of the cellulose fibres, and a second outlet located at the larger end of said separating chamber in axial alignment with said first-mentioned outlet and through which is discharged a second stream of the suspension containing a major portion of the cellulose fibres, including an ejector through which the suspension and air are discharged from said vacuum chamber, said ejector serving to maintain a vacuum in the liquid-free space of said chamber and in the liquid-free core of the vortex in the separating chamber, and a suction conduit having one end connected to said ejector and the other end extending into the end of the liquid-free core remote from the apex end of the conical separating chamber.

5. Apparatus for de-aerating an aqueous suspension of cellulose fibres and separating dirt particles therefrom, comprising a conical separating chamber in which the suspension is whirled about a central axis to produce a vortex of conical form having a central liquid-free core, a tangential inlet through which the pulp suspension is continuously fed into the larger end of said chamber to establish and maintain said vortex, an axial outlet at the apex end of said chamber, a vacuum chamber affording a liquid-free space into which air entering said liquid-free core is discharged together with a stream of the suspension containing dirt particles and a minor proportion of the cellulose fibres, and a second outlet located at the larger end of said separating chamber in axial alignment with said first-mentioned outlet and through which is discharged a second stream of the suspension containing a major portion of the cellulose fibres, including an ejector through which the suspension and air are discharged from said vacuum chamber, said ejector serving to maintain a vacuum in the liquid-free space of said chamber and in the liquid-free core of the vortex in the separating chamber and a suction conduit having one end connected to said ejector and the other end extending into the end of the liquid-free core remote from the apex end of the conical separating chamber, said suction conduit being centered with respect to the central longitudinal axis of the separating chamber and having an internal diameter slightly less than the diameter of said liquid-free core.

6. Apparatus for tie-aerating an aqueous suspension of cellulose fibres and separating dirt particles therefrom, comprising a conical separating chamber in which the suspension is Whirled about a central axis to produce a vortex of conical form having a central liquid-free core, a tangential inlet through which the pulp suspension is continuously fed into the larger end of said chamber to establish and maintain said vortex, an axial outlet at the apex end of said chamber, a vacuum chamber affording a liquid-free space into which air entering said liquid-free core is discharged together with a stream of the suspension containing dirt particles and a minor proportion of the cellulose fibres, and a second outlet located at the larger end of said separating chamber in axial alignment with said first-mentioned outlet and through which is discharged at second stream of the suspension containing a major portion of the cellulose fibres, including an ejector through which the suspension and air are discharged from said vacuum chamber, said ejector serving to maintain a vacuum in the liquid-free space of said chamber and in the liquidfree core of the vortex in the separating chamber, and a suction conduit having one end connected to said ejector and the other end extending into the end of the liquidfree core remote from the apex end of the conical separating chamber, said conduit being centered with respect to the central longitudinal axis of the separating chamber and having an internal diameter greater than the diameter of said liquid-free core.

References Cited in the file of this patent UNITED STATES PATENTS 2,377,524 Samson et al June 5, 1945 2,571,219 De Cew Oct. 16, 1951 2,878,934 Tomlinson Mar. 24, 1959 

